Potash ore beneficiation process



tates The present invention relates generally to a process for beneficiating ores and particularly to a process for beneficiating potash ores. More particularly the present invention relates to a process for beneficiating potash salts comprising langbeinite, sylvite and halite using an air tabling operation.

As is well known, potash is of great economic importance. The sources of potash are very numerous. Extensive deposits of potash salts are found on every continent. However, in practically no instance is the potash salt found as a substantially pure salt. On the North American continent, one frequently encountered potash salt is sylvite (KCl). The KCl is not often found in any appreciable quantities as pure sylvite ore but is most often found as the sylvinite ore, which is a mixture of KCl and NaCl. Sylvinite ores sometimes have a high purity of approximately 96%, and a typical analysis of such an ore is as follows:

Percent Sylvite (KCl) 31 Halite (NaCl) 65- Other constituents or impurities consisting of silicates,

sulfates, etc 4 The sylvite values of ores of such a high purity may readily be recovered or concentrated by various concentration processes, such as crystallization, electrostatic separation, flotation separation, etc. As the natural deposits of ores of such high purity are depleted, it has been necessary to resort to ores of less purity. In some instances, however, it has been found that the impurity in the ore is troublesome in the concentration process. Langbeinite (K SO '2MgSO is a commonly occurring impurity in sylvinite ores and at relatively high concentrations of langbeinite it is often difiicult to separate or concentrate the sylvite values in the potash ore.

A typicalanalysis of such an ore is as follows:

Percent Sylvite (KCl) 10.6 Halite (NaCl) 53.2 Langbeinite (K SO -2MgSO 33.9 Other constituents or impurities 2.3

Accordingly, it is an object of the present invention to provide a process for beneficiating a potash ore containing langbeinite.

It is another object of the present invention to provide a process for beneficiating a potash ore containing langbeinite to obtain a concentrate of increased potash concentration and decreased langbeinite concentration.

A further object of the present invention is to provide a process for beneficiating a sylvite-halite ore containing langbeinite in an amount greater than 7% by weight, to obtain a concentrate containing sylvite in an increased concentration and langbeinite in an amount less than 7% by weight. 7

.These and other objects and advantages of the present invention will be apparent to those skilled in the art as the description of the present invention progresses.

In accordance with the present invention, it has been discovered that eminently satisfactory dry beneficiation of ores and minerals can be achieved through air tabling by means of a series of critical and interdependent process steps. Generally described, a potash ore containing l'angbeinite is first comminuted to substantially liberate atet Patented Oct. 3, 19611 2 the particles of the ore. The comminuted ore is then' subjected to an air tabling operation, whereby a concentrate is obtained which has a higher potash concentration and a lower langbeinite concentration than the original ore. This concentrate is then sized to produce a fraction whose average particle size is larger than the average particle size of the concentrate. It has been found that this larger size fraction has a higher potash concentration and a lower langbeinite concentration than the concentrate recovered from the tabling operation.

In this novel process, potash ore containing langbeinite, for example sylvinite ore containing langbeinite as received from the mine, is comminuted to economical liberation size to produce a granular feed material. The comminution of the ore to the liberation of the various constituents to be separated is eifected to liberate a substantial amount of the various constituents. It may be desirable or economical to comminute the ore to liberate all of the constituents, however, the ore may be liberated to a lesser extent, for example to -80% liberation. This granular material is sized to produce a granular feed of a particle size in the range of about -8 mesh and preferably a feed consisting of 8+200 mesh particles and still more preferably a feed consisting of -8+150 mesh particles. The cornminution of the ore may be carried out in a ball mill, roller mill, hammer mill, or any other suitable type of grinding or crushing apparatus. When the ore is ground to the mesh size indicated above, the sylvite values, the halite values and the langbeinite values are substantially separated from each other and the ore is ready for further treatment in accordance with this invention.

After the comminution step of the process the ore may be passed directly to the air tabling zone or it may be sized before the air tabling operation. It is frequently desirable to size the ore prior to the air tabling operation since a sized feed in an air tabling operation results in a greater screen load or sizing load and a smaller table load.

The screened ore is then passed to an air tabling zone wherein the ore is subjected to an air tabling operation. A sylvite concentrate is separately recovered from the air tabling zone and a langbeinite concentrate is also separately recovered from the air tabling zone. While the operation is herein described as producing only two fractions or concentrates, it is to be understood that other fractions may also be produced in the air tabling zone. For example, a so-called mids fraction is usually produced and is most often recycled to the tabling zone in admixture with the fresh feed.

In the air tabling zone the comminuted potash ore is subjected to an air tabling operation. An air table is a shaking table in which air blown through a porous deck, which is preferably rifiled, meets with the shaking to fiuidize a layer of dry solids moved lengthwise of the deck by a quick-return shake. The deck of the apparatus is canted somewhat on the longitudinal center line. The granular friction of the lighter gravity particles is overcome by the continual impingement of low-pressure air on the lower surface of the particles, thereby giving them fluidity, the velocity of the air being maintained to a degree that only the lighter gravity particles are affected. The semi-fluid mass formed on the deck stratifies and moves lengthwise on the deck due to the quiclereturn shaking action and moves downslope on the canted deck under the influence of gravity. The concentrates and other fractions are removed at the edge of the deck. Air tabling apparatus of this type is well known. Examples of commercially available air tables are the Sutton Steele table, known as the airfioat or Kupp-Kelly table, the Birtley table, and the Knapp and Bates (K and B) table. Air jigs or tables similar to the "Roberts and Schaefer airflow coal cleaner are also effective.

Factors to be considered in an air tabling operation are: the extent of the spread of air as it leaves the deck and impinges upon the mineral particle, the velocity of the air impinging on the particles, the size of the particles, the range of particle sizes, and the shape of the particles.

The langbeinite oreparticles have aspecific gravity of from about 2.6 to about 3.1 and are relatively heavier than the sylvite and halite ore particles, which have a specific gravity of from about 1.7 to about 2.3. A langbeiniteconcentrate and a sylvite concentrate are, therefore, separately recovered in the air tabling operation.

The langbeinite concentrate obtained from the air tabling operation, when compared with the ore charged to the tabling zone, has a substantially higher langbeinite concentration and a substantially lower sylvite concentration. The langbeinite concentrate may be recovered as a product or may be additionally concentrated in a further concentrating operation.

Similarly, the sylvite concentrate obtained from the air tabling operation, when compared with the ore charged to the tabling zone, has a substantially higher sylvite concentration and a substantially lower langbeinite concentration. It has been found that when'the sylvite concentrate is sized to produce a larger sized fraction, that is, a fraction whose average particle size is larger than the average particle size of the concentrate, that the larger sized fraction has a still higher sylvite concentration and still lower langbeinite concentration. Iherefore, in accordance with the present invention, the sylvite concentrate is subjected to a sizing operation. Any suitable type of sizing such as sedimentation, elutriation, screening, etc. may be used and a screening operation has proven to be very satisfactory. .It has heen found preferable to size the sylvite concentrate so as to produce a substantially +50 mesh size fraction and a substantially 50 mesh size fraction. A sizing around the 50 mesh size is preferred since the +50 mesh .Size fraction has been found to be very high in sylvite concentration and relatively low :in langbeinite concentration. A separation around a mesh size different than 50 may be used; however, the sizing will preferably be done about a mesh size within the range of from about mesh to 80 mesh, that is, the small size limit for the larger size fraction will be within therange of from about 20 mesh to about 80 mesh. .It is also within the scope of this invention to size the sylvite concentrate from the air tabling zone so as to-produce more than two ized fractions.

It has further been found that the smaller sized fractionrecovered from the above screening operation may have the constituents substantially separated when it is subjected to another air tabling operation. The air tabling operation on the smaller sized fraction is generally similar to the air tabling of the original potash ore. The average size of the particle is, however, smaller because of the sizing operation. Accordingly, it may be necessary to decrease the flow rate of air through the deck of the table and make other adjustments so as to obtain optimum separation of the components of the ore. A langbeinite concentrate and a sylvite concentrate are separately recovered from the air tabling operation on the smaller sized particles.

The langbeinite concentrate obtained from this latter air tabling operation, when compared with the smaller sized fraction charged, has a substantially higher langbeinite concentration and a substantially lower sylvite concentration. This langbeinite concentrate may be mixed with the langbeinite concentrate obtained in the first tabling operation. Similarly, the sylvite concentrate obtained from the air tabling of the smaller sized fraction, when compared with the charge to this air tabling zone, has a substantially higher sylvite concen- Example Natural sylvinite ore from the Carlsbad section of New Mexico was comminuted in a roll crusher and then in the hammer mill. The comminuted ore was screened to produce a -8 mesh fraction. Substantially all of the fraction contained particles in the range of -8 mesh to about 200 mesh size. The fraction had the following analysis:

Percent Langbeinite 33.89 KCl 10.61 Remainder, mostly .NaCl 55.50

This fraction was subjected to a tabling operation using 21 Sutton and Steele model V air table. A sylvite concentrate and a langbeinite concentrate were separately recovered. The sylvite concentrate was 40.4% by weight of the original charge and the langbeinite concentrate was 59.6% by weight. The analyses of these fractions were as follows:

Sylvite concentrate: Percent Langbeinite 12.5 KCl 18.0

Langbeinite concentrate:

Langbeinite 48.4 KCl 5.5

The sylvite concentrate was then sized at 50 mesh (Tyler screen size) and a +50 mesh fraction and a -50 mesh fraction were separately recovered. The -50 mesh fraction was 19.9 weight percent of the original sylvinite or charged to the tabling operation and the +50 mesh fraction was 20.5%. The analyses of these fractions were as follows:

-50 mesh: Percent Langbeinite 15.7 KCl 16.4

+50 mesh:

Langbeinite 5.1 KCl 21.6

It may be noted that the +50 mesh fraction is higher in KCl concentration than the sylvite concentrate obtained from the air tabling operation.

The 50 mesh fraction was then air tabled on the same air table originally used and a sylvite concentrate and a langbeinite concentrate were separately recovered. The sylvite concentrate recovered from this second tabling operation was 15.3% by weight of the original sylvinite ore fed to the first tabling operation and the langbeinite concentrate recovered from this second tabling operation was 4.6% by weight. The analyses of these concentrates were as follows:

Sylvite concentrate: Percent Langbeiuite 9.0 KCl 1.6.8 Langbeinite concentrate:

Langbeinite 39.2 KCl 6.2

This sylvite concentrate was combined with the +50 mesh fraction obtained from the screening operation and this combined sylvite concentrate represented 35.8% by weight of the original ore charged to the process and had the following analysis:

Percent Langbeinite 6.7

KCl 19.0

Percent Langbeinite 48.7 KCl 5.7

This example illustrates that following the procedure of this invention a sylvite concentrate containing less than 7% by weight of langbeinite may be prepared from a sylvinite ore containing more than 7% and as much as 30% by weight of langbeinite.

The description of the invention utilized specific reference to certain process details; however, it is to be understood that such details are illustrative only and not by way of limitation. Various modifications and equivalents of the invention will be apparent to those skilled in the art from the foregoing description.

Having now fully described and illustrated the invention, what is desired to be secured and claimed by Letters Patent is set forth in the appended claims:

1. A process for beneficiating a potash ore containing sylvite, langbeinite and halite constituents which comprises comminuting the ore to the liberation of the various constituents, subjecting the comminuted ore to an air tabling operation and recovering a sylvite concentrate, and sizing said concentrate and recovering a large size fraction of increased sylvite concentration from the sizing operation.

2. A process for beneficiating a potash ore containing sylvite, halite and langbeinite constituents, the langbeinite concentration being greater than 7% by weight, Which comprises comrninuting the ore to the liberation of the various constituents, subjecting the cornminuted ore to an air tabling operation and recovering a sylvite concentrate, sizing said concentrate and recovering a large size fraction having increased sylvite concentration and having a langbeinite concentration of less than 7% by weight from the sizing operation.

3. A process for beneficiating a potash ore containing sylvite, halite and langbeinite constituents which comprises comminuting the ore to produce a -8 mesh fraction, subjecting the 8 mesh fraction to an air tabling operation and recovering a sylvite concentrate, sizing said concentrate and recovering a larger sized fraction of increased sylvite concentration having the smaller size limit Within the range of from about 20 mesh to about 80 mesh.

4. A process for beneficiating a potash ore containing sylvite, halite and langbeinite constituents, the langbeinite concentration being greater than 7% by weight, which comprises comminuting the ore to produce a 8 mesh fraction to liberate the various constituents of said ore, subjecting said 8 mesh fraction to an air tabling operation and recovering a sylvite concentrate, sizing said concentrate and recovering a larger sized fraction having the smaller size limit within the range of from about 20 mesh to about 80 mesh, having increased sylvite concentration and having a langbeinite concentration of less than 7% by weight.

5. A process for beneficiating a potash ore containing sylvite, langbeinite and halite constituents which comprises comminuting the ore to the liberation of the various constituents, subjecting the comminuted ore to an air tabling operation and recovering a sylvite concentrate, sizing said concentrate and recovering a large size fraction of increased potash concentration and a smaller size fraction from the sizing operation, air tabling said smaller size fraction and separately recovering a fraction of increased sylvite concentration and a fraction of increased langbeinite concentration.

6. A process for beneficiating a potash ore containing sylvite, halite and langbeinite constituents, the langbeinite concentration being greater than 7% by weight, which comprises comminuting the ore to the liberation of the various constituents, subjecting the comminuted ore to an air tabling operation and recovering a sylvite concentrate, sizing sai-d concentrate and recovering a large size fraction having increased sylvite concentration and having a langbeinite concentration of less than 7% by Weight and a smaller size fraction from the sizing operation, air tabling said smaller size fraction and separately recovering a fraction of increased sylvite concentration and a fraction of increased langbeinite concentration.

7. A process for beneficiating a potash ore containing sylvite, halite and langbeinite constituents which comprises comminuting the ore to produce a 8 mesh fraction, subjecting the 8 mesh fraction to an air tabling operation and recovering a sylvite concentrate, sizing said concentrate and separately recovering a larger sized fraction of increased sylvite concentration having the smaller size limit within the range of from about 20 mesh to about 80 mesh and a smaller size fraction, air tabling said smaller size fraction and separately recovering a fraction of increased sylvite concentration and a fraction of increased langbeinite concentration.

8. A process for beneficiating a potash ore containing sylvite, halite and langbeinite constituents, the langbeinite concentration being greater than 7% by weight, which comprises comminuting the ore to produce a -8 mesh fraction to liberate the various constituents of said ore, subjecting said 8 mesh fraction to an air tabling operation and recovering a sylvite concentrate, sizing said concentrate and separately recovering a larger sized fraction having the smaller size limit within the range of from about 20 mesh to about 80 mesh having increased sylvite concentration and having a langbeinite concentration of less than 7% by weight and a smaller sized fraction, air tabling the smaller size fraction and separately recovering a fraction of increased sylvite concentration and a fraction of increased langbeinite concentration.

References Cited in the file of this patent UNITED STATES PATENTS 1,939,119 Holt et a1 Dec. 12, 1933 2,175,484 Rees et a1. Oct. 10, 1939 2,307,064 Patterson Jan. 5, 1943 2,330,479 Erickson Sept. 28, 1943 2,347,215 Pattee Apr. 25, 1944 2,487,845 Bird Nov. 15, 1949 2,745,547 Werge May 15, 1956 2,849,113 Bourne et al. Aug. 26, 1958 OTHER REFERENCES Taggart: Handbook of Mineral Dressing, 1945, see. 11, pages and 73. 

1. A PROCESS FOR BENEFICIATING A POTASH ORE CONTAINING SYLVITE, LANGBEINITE AND HALITE CONSTITUENTS WHICH COMPRISES COMMINUTING THE ORE TO THE LIBERATION OF THE VAROUS CONSTITUENTS, SUBJECTING THE COMMINUTED ORE TO AN AIR TABLING OPERATION AND RECOVERING A SYLVITE CONCENTRATE, AND SIZING SAID CONCENTRATE AND RECOVERING A LARGE SIZE FRACTION OF INCREASED SYLVITE CONCENTRATION FROM THE SIZING OPERATION. 